The subject of the present invention is a cannon breech comprising a breech block that is mobile between the two cheeks of a breech ring.
Another subject of the invention is the cannon comprising such a breech.
Among the different known types of breech, the subject of the present invention is that of a cannon breech in which the breech block comprises on each of its sides and opposite the corresponding cheek of the breech ring at least one bearing element having at least one bearing surface paired with a matching bearing element of the cheek. In bearing upon the paired surface, strain generated during firing of a round is transmitted to the cheek.
In a very common embodiment, a simple bearing between the breech block and the breech ring is used. The breech block has on its rear face, on either side of this face, a bearing surface that is substantially perpendicular to the common axis of the barrel and the breech. The bearing surface also bears upon a bearing surface paired with the corresponding cheek of the breech ring. The plane of these surfaces intersects the plane defined by the axis of the barrel and the horizontal line following a perpendicular line to the axis.
When a round is fired, the combustion of the powder in the barrel chamber generates very high pressure gases that act both on the front face of the breech block, which closes when the breech is opened, and on the round that is thereby expelled at an extremely high velocity.
The pressure withstood by the breech block generates a load over the front face of the block wherein the resultant is located along the axis of the barrel and of the breech. This load is transmitted to the breech ring by the afore-mentioned bearing surfaces. In addition to the longitudinal traction strain, the lateral off-set of the bearing surfaces with respect to the neutral axis of each of the cheeks induces in each of the checks a bending moment that tends to force the cheeks apart from one another.
To avoid opening the cheeks of the breech ring under the action of this strain, the two cheeks are linked together by a brace located in the lower rear part of the ring. The brace fulfils another function in that it ensures the guidance of the round during loading of the round.
This structure has a great disadvantage because the useful bearing surface area of the breech on the cheek is limited, which also limits the strain that may be transmitted to the cheek and therefore limits the maximum pressure that may be generated inside the barrel. Moreover the problem of overall bulk prevents the cheeks from being increased in size, notably those following the axis of the barrel.
Another structure comprising several bearings so as to better spread the strain in the cheeks of the breech ring is known by document US-A-5014 592, where it is also known to eliminate the brace so as to facilitate machining of the ring.
In this event, a third bearing is required to reduce the opening of the cheeks of the breech ring if the brace is eliminated. This necessitates the breech block to be increased in size following the axis of the barrel, which may constitute a serious handicap in all cases where available space is very limited.